Volume control system



L E H C S T N E H R E VOLUME CONTROL SYSTEM Filed June 21, 1930 2Sheets-Sheet 1 IN VEN TOR.

A TTORN y 1934- E. R. HENTSCHEL VOLUME CONTROL SYSTEM 2 Sheets-Sheet 2Filed June 21, 1930 INVENTOR. Mafia y Patented May 15, 1934 UNITEDSTATES T FFEQE VOLUME CONTROL SYSTEM Application June 21, 1930, SerialNo. 462,904

11 Claims.

i vide a circuit arrangement for automatically con trolling the volumeof sound reproduced by a radio receiver independently of fading effects.

Another object of my invention is to provide a circuit arrangement for aradio frequency amplification system in a radio broadcast receiverwhereby resistance may be automatically introduced into the circuits ofthe radio frequency amplifier when the incoming signaling energyincreases in strength and the resistance reduced to normal values whenthe signaling energy is of normal amplitude.

Still another object of my invention is to provide a circuit arrangementwhereby a resistance interposed in the radio frequency circuits of aradio receiver may be normally activated to maintain the resistance in acondition in which it is immediately responsive to an increase ineffective value upon increase in the amplitude of the received signalingenergy for maintaining the reproduced sound at substantially'constantvolume.

A further object of my invention is to provide an arrangement ofresistances which maybe interposed in the resonant circuits of a radiofrequency amplifier in a radio receiving system in such position thatthe resistance is subjected to heating eifects by the incoming signalingenergy for introducing resistance in the circuits of the receivingsystem upon increase in amplitude of the incoming signaling energy forcompensating for changes in the amplitude of the signaling energy andmaintaining the volume of reproduced sound substantially constant.

Other and further objects of my invention reside in the volume controland circuit arrangement as described more fully in the specificationhereinafter following'by reference to the accompanying drawings, inwhich:

'Fig. 1 diagrammatically illustrates the circuit of my invention appliedto a radio broadcast receiver and Fig. 2 illustrates a modified form ofcontrolcircuit embodying the principles of my invention.

My invention employs means for automatically reducing the amplitude ofcurrent in one or more of the radio frequency amplification stages of aradio receiver when the incoming signaling energy becomes too strong. Iarrange a resistance in circuit with one or more of the radio frequencyamplifier stages and provide a connec tion from the output circuit ofthe final stage of amplification by which the temperature condition ofthe resistance may be controlled in proportion to the amplitude of thecurrent in the sound reproducer circuit. Under normal values orconditions of this resistance there is substantially negligible effectupon incoming signaling energy. However, under conditions of fading thesignaling energy may rise to greater proportions thus increasing thetemperature of the resistance and correspondingly increasing theeffective value of the resistance. The resistance thus interposed in theradio frequency amplification system tends to reduce the amplitude ofthe signaling energy which passes therethrough thus reducing the volumeof the reproduced sound. As the volume of the reproduced sound decreasesthe temperature condition of the resistance device is reduced to normaland the effective resistance thereof correspondingly reduced, allowingthe signaling energy which is supplied to the reproducer circuit to bemaintained at normal.

Referring to the drawings in more detail, reference character 1designates an antenna system connected with primary winding 2 of atransformer system having secondary winding 3, constituting part of aresonance circuit tuned by variable condenser 4 and connected to theinput circuit of electron tube 5, which constitutes the first stage ofradio frequency amplification for the receiving circuit. The receiverincludes a second stage of radio frequency amplification constituted byelectron tubes 6, a succeeding stage of radio frequency amplificationincluding electron tube '7, a detector tube 8 and two stages of audiofrequency power amplification indicated at 9 and 10. The several stagesof the radio frequency amplifier and detector are suitably coupledthrough the transformers 11, 12 and 14. The audio frequency poweramplifier circuits are coupled through transformers 15 and 16,respectively. Each stage of radio frequency amplification and thedetector is tuned as designated at 4, 17, 18 and 19. The soundreproducer is indicated at 20 connected in the output of the final stageof power amplification. I provide an audio frequency transformer 21having its primary winding 22 connected in series with the soundreproducer 20 in the sound reproducing circuit. The transformer 21 has asecondary winding 23 which is connected through the conductors 24 withthe resistance bridge circuit designated at 25. The bridge circuitresistance comprises arms 25a, 25b, 25c and 25d connected as shown. Theresonance circuit including the secondary Winding of transformer 11 andtuning condenser 1'7 constitutes a tank circuit and is disposed inseries with the resistance bridge circuit across the terminals 27 and 23thereof. The leads 24 connect to the resistance bridge circuit acrossthe terminals 29 and 30 thereof. Radio frequency choke coils 31 and 32are disposed in circuit with the leads 24 for preventing radio frequencycurrents from passing to the audio frequency control circuit. Thetransformer 21 has a tapped secondary winding 23 wherein the taps areconnected to the adjustable switch 45. The tap 45a entirely eliminatesthe secondary winding 23 thus rendering the operation of the setindependent of the automatic control feature. The adjustable switch 45enables the volume control circuit to be adjusted to a selectedoperating point by varying the amount of audio frequency heating currentsupplied to the compensating resistance.

The power supply system for the circuits of the receiving apparatus leadfrom the primary connection 33 through the transformer system 34,rectifier 35, filter circuit 36 to the potentiometer circuit 37 fromwhich taps are taken to the several power circuits of the receiver.

In order to maintain the resistance device in a sensitive condition sothat it will respond rapidly to a resistance change due to a temperaturechange under conditions of increase in signal amplitude, I introduce incircuit with the resistance, a predetermined normal potential. Thisenergy is obtained from the potentiometer 3'7 and in Fig. 1 I have shownthe manner of obtaining this potential by means of taps 40 and 41 onpctentiometer 3'7, which taps are disposed in series with the audiofrequency control circuit 24 with condenser 42 disposed in shuntthereto. The connection to the common cathode return lead extends fromone end of the resonance circuit which contains the secondary winding11b of the coupling transformer 11.

The grid bias circuit is completed through choke coils 31 and 32 andresistors 25c and 25d to taps 40 and 41 on potentiometer 37 through thesecondary winding 23 of transformer 21. The resistance of thetransformer secondary 23 is small as compared to both resistors 25c and25d and the portion of potentiometer 3'7 between taps 40 and 41 andtherefore will not affect the bias potential nor the value of the directcurrent which maintains the resistance bridge circuit at operatingtemperature. Condenser 44 completes the radio frequency path in thetuned input circuit returning to the cathode in tube 6. An example ofthe values of the resistances employed in the compensation system is asfollows: The radio frequency inductance 11b of the coupling transformeris constructed with a high degree of efiiciency having as small a radiofrequency resistance as possible. This coil, as well as the othercoupling coils in the radio frequency amplifier is wound with conductorhaving a minimum radio frequency resistance. For example at very highfrequencies solid conductor is to be preferred whereas within thebroadcast band litzendraht conductor is to be preferred. The resistanceof secondary inductance 11b may be for example approximately 10 ohms. Asimilar resistance is effective across the resistance bridge, that iseach resistance member 25a, 25b, 25c and 250? has a value of 10 ohmswhen operating at normal signal intensity and subject to the passage ofcurrent from taps 40 and 41 along the potentiometer 37. Condenser 44 hasa capacity of approximately .001 mid. Condenser 42 has a value of 1 mfd.

In Fig. 2 I have shown a modified circuit arrangement wherein theelectron tube 6 has its input circuit connected with the tuned resonancecircuit including variable condenser 1'7 with the variable resistancemember 38 disposed directly in series therein. The leads 24 from theaudio frequency control circuit which connect through transformer 21with the output circuit of the final stage of power amplification,convey variable energy to resistance 38 through the choke coil 39 andvariable tap 38a. Tap 38a may be selectively positioned along resistance38 in order to regulate the amount of volume control which may beobtained. As the amplitude of the current increases through the soundreproducer 20 the current flow through the audio frequency controlcircuit increases and the current through the resistance 38 increasesraising the temperature thereof and increasing the resistance so thatthe effective strength of the incoming signaling energy may be reduced.

The normal temperature regulating current passes through resistance 38from taps 40 and 41 on potentiometer 3'7 as hereinbefore explained inconnection with Fig. 1. The bias potential which is applied to the gridelectrode of tube 6 is a potential intermediate the potential alongresistance 3'7 at'either tap 40 of 41. The amount of current normallypassed through the resistance bridge 25 or the resistance device 38 isregulated by selectively positioning taps 40 and 41 on potentiometer 37.The resistance element 38 or the resistance elements of the resistancebridge 25 are brought up to a sensitive condition by the passage ofcurrent therethrough so that upon increase in current due to fadingeffects the temperature rise increases the effective resistance of theresistance members and decreases the volume of sound from the soundreproducer 20.

The compensation circuit may be disposed in any one or more of thestages of radio frequency amplification. Various modifications may bemade in the circuit arrangements and it will be understood that rapidchanges in fluctuations of sound will not serve to change the effectiveresistance of the amplification circuit to a sufficient extent to changethe value of reproduced sound. The effective resistance changes onlyunder a condition of gradual volume change such as is brought aboutunder conditions of fading. The wire constituting the resistanceelements is selected for required resistance values and in order toinsure more rapid response the resistance elements may be mounted withina vacuum of selected value. The greater the vacuum the more rapid willbe the control action. The compensation system of my invention insuresreproduction of sound at uniform volume adding to the quality andenjoyment of radio broadcast programs.

While I have described my invention in certain preferred embodiments, Idesire that it be understood that modifications may be made and that nolimitations upon my invention are intended other than are imposed by thescope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. An amplification system comprising a plurality of electron dischargedevices coupled one to another, resonant circuits connected with each ofsaid electron discharge devices and means disposed in series in one ofsaid resonant circuits for automatically controlling the amplificationcharacteristics of one or more of said electron discharge devices inaccordance with variations in the signal output of said electrondischarge devices.

2. An amplification system including a multiplicity of thermionic tubecircuits coupled one to another and thermally responsive means connectedin series in the resonant circuit connecting with one of said tubecircuits and controlled by a succeeding thermionic tube circuit forvarying the effective resistance of said preceding selected tubecircuits according to the amplitude of the reproduced signaling energyin the circuit of said succeeding electron tube circuit.

3. An amplification system including a plurality of electron tube radiofrequency amplification stages, tuned circuits connected therewith, anamplification system, an impedance device connected in series in aselected tuned circuit, and means connected with said amplificationsystem for energizing said impedance device according to the amplitudeof the reproduced signaling energy for controlling the effectiveresistance of said selected tuned circuit.

4. A volume control system for amplifiers comprising in combination witha multiplicity of amplification stages, coupling circuits intermediatesaid stages, tuning means for said coupling circuits, resistanceelements disposed in circuit with the tuning means in one of saidcoupling circuits, a circuitous path from one of said amplificationstages to said resistance elements for subjecting said resistanceelements to the effects of a thermal current proportional to theintensity of the reproduced signaling energy for correspondinglycontrolling the effective resistance of the coupling circuit containingsaid resistance elements and maintaining the volume of reproduced soundsubstantially constant.

5. In a radio receiving system a multiplicity of electron dischargedevices, resonant circuits connected therewith, a resistor in one ofsaid resonant circuits, and means for effecting a change in theresistance of said resistor in accordance with variations in signaloutput of the receiving system.

6. In a signal receiving system a multiplicity of electron tubes,resonant circuits connected therewith, a resistor in the form of abridge connected in one of said resonant circuits, and means forsubjecting said bridge to heating current in accordance with currentchanges through a succeeding electron tube for changing the effectiveresistance of said bridge and correspondingly controlling the amplitudeof current through said succeeding electron tube.

7. A volume control system for amplifiers comprising in combination witha multiplicity of amplification stages, coupling circuits intermediatesaid stages, tuning means for certain of said stages, resistanceelements disposed in circuit with the tuning means in one of saidcoupling circuits, means for passing heating current continuouslythrough said resistance elements, a circuitous path from one of saidamplification stages to said resistance elements for subjecting saidresistance elements to the effects of a thermal current proportional tothe intensity of the reproduced signaling energy for correspondinglycontrolling the efiective resistance of the coupling circuit in whichsaid resistance elements are connected and maintaining the volume ofreproduced sound substantially constant.

8. A signal amplification system comprising a multiplicity of electrontube amplification stages interconnected one with another, tuning meansfor certain of said stages, a resistance member disposed in series withthe tuning means in one of said electron tube amplification stages,means for varying the conductivity of said resistance member accordingto the change in volume of the reproduced signaling energy and means fordetermining the normal effective value of said resistance.

9. A signal amplification system comprising a multiplicity of electrontube amplification stages interconnected one with another, an inductanceand capacity path for tuning certain of said amplification stages, aresistance member disposed in circuit with the inductance and capacitypath in one of said electron tube amplification stages, means forvarying the conductivity of said resistance member according to thechange in volume of the reproduced signaling energy and means forsubjecting said resistance to the passage of a continuous heatingcurrent for fixing the normal conductivity of said resistance wherebythe effective resistance of said amplification stages to the passage ofsignaling energy may be controlled.

10. A signal amplification system comprising a multiplicity of electrontube amplification stages interconnected one with another, means fortuning certain of said stages, a resistance member disposed in circuitwith the tunin means in one of said electron tube amplification stages,a circuit for subjecting said resistance member to the passage of acontinuous heating current and means for superimposing a variablecurrent upon said resistance proportional in amplitude to the volume ofthe reproduced signaling energy for correspondingly varying theeffective value of said resistance member.

11. A signal receiving system comprising a multiplicity of electron tubeamplification stages, a resistance member connected in circuit with oneof said amplification stages, a circuit including a transformerconnected with a succeeding amplification stage for supplying heatingcurrent to said resistance member, and means for selectively fixing theratio of said transformer for controlling the amount of heating currentsupplied to said resistance member.

ERNEST R. HENTSCHEL.

